CAPI = low conversions

Hi,

I have notice a drop in conversions each time I connect the CAPI, its like it throttles Facebook traffic somehow , once I disconnect it everything goes back to normal and conversions go up, but then it does not count all purchases in the pixel.

No CAPI = good conversion (good traffic) , low count in purchase event.
With CAPI = low conversions (low traffic), all conversions counted.

I wonder does consent cookies are needed alongside CAPI to work properly.

At the moment I only have cookie notice ( ex. This site uses cookies).

Any help will be much appreciated.